SOLUTION: There are 20 multiple choice questions on a test with 5 possible answers each. Find the probability of guessing 15 questions out of 20 correct. Is this likely or unlikely? Why?

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Question 655299: There are 20 multiple choice questions on a test with 5 possible answers each. Find the probability of guessing 15 questions out of 20 correct. Is this likely or unlikely? Why?
Currently, I have calculated:
P(15 correct out of 20 questions)= 20/15 (.20)^15 (.80)^5
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

Note: The probability of x successes in n trials is: 

P = nCxp%5Ex%2Aq%5E%28n-x%29 where p and q are the probabilities of success and failure respectively. 

In this case, Yes!  p = .20 & q = .80

P(15 correct out of 20 questions)= 20C15 (.20)^15 (.80)^5 = 15,504(.20)^15 (.80)^5= .00000017

Probability so...small, UNLIKELY